In fluid-flow machines, such as in gas or steam turbines for example, component gaps cause the formation of bleed or leakage flows. This involves part of the working fluid of the main flow, which flows along a flow channel through the fluid-flow machine, penetrating into the component gaps adjacent the flow channel and escaping via these component gaps. Such component gaps that open out into the flow channel exist for example between platform-like shroud elements of the blading, which, arranged in series, form an inner or outer delimiting wall of the flow channel.
Bleed or leakage flows are generally undesired, since they no longer provide any contribution to the energy conversion and consequently, as a loss of the main flow, have to be balanced. Furthermore, in particular downstream of a combustion chamber, the working fluid is very hot. Bleed or leakage flows which originate from this hot flow are accordingly similarly very hot and can cause excess temperatures of the components adjacent the component gaps as a result of heat transfer.
In order to minimize bleed or leakage flows, it is usually attempted in the structural design to make the component gaps as small as possible. However, in the hot gas region in particular, minimum gaps between the components are often required to allow compensation for temperature-induced expansions of the components.
To minimize the bleed or leakage flows, it is therefore necessary to take suitable measures to seal the component gaps that are sometimes necessary for the purposes of expansion compensation against undesired penetration of working fluid. For example, for this purpose a cooling or sealing fluid may be blown out from the component gap concerned. The cooling or sealing fluid that is blown out fills the component gap and thereby prevents working fluid from penetrating into the component gap. In order also to be able to effectively prevent local flowing-in of working fluid into the component gap, the cooling or sealing fluid must however be blown out both in an adequate amount and with a sufficient positive pressure with respect to the working fluid. In particular in the region of the turbine inlet of a fluid-flow machine, the requirement for sufficient positive pressure of the cooling or sealing fluid is often not met, since the cooling or sealing fluid is usually branched off from the region of the compressor of the fluid-flow machine, and accordingly has only a low positive pressure. To assist the sealing effect and to minimize the required amount of cooling or sealing fluid, a strip seal is therefore often additionally placed into the component gap. For this purpose, the strip seal is arranged in the component gap in such a way that it at least constricts or largely blocks the component gap.
Such strip seals are known for example from EP 1 306 589 or DE 2 135 695.
In EP 1 306 589, a metallic, single- or multi-layer seal is described, comprising a half-open, singly or multiply curved profile, which is clamped into the gap to be sealed. The seal extends over the entire length of the component gap.
DE 2 135 695 discloses a sealing ring with a C-shaped cross section, in the case of which an annular spring is arranged between the legs to spread the sealing ring. Here, too, the seal extends over the entire length of the component gap.
By means of such strip seals, it would indeed be possible to seal a component gap virtually completely. However, in particular for cooling the components adjacent the component gap or for cooling the sealing element, it is often necessary to allow a certain throughput of cooling fluid through the component gap. In these cases, the aforementioned strip seals may be provided with openings, through which cooling fluid which is supplied to the component gap on the side of the component gap facing away from the working fluid flow is carried away into the main flow of the working fluid. For this purpose, a delivery pressure of the cooling fluid in the component gap has to be provided in such a way that a pressure gradient in the direction of the working fluid is ensured radially over the seal. If, however, the formation of a locally and temporally restricted positive pressure of the working fluid occurs during operation, there is the risk of the pressure gradient also being reversed. Hot working fluid is then at least temporarily forced out of the main flow into the component gap, and can lead here to material overheating of the components adjacent the component gap or else of the seal itself. A local positive pressure can be brought about for example by the blade tip running past the component gap and the pressure wave caused by this.